The only good reason to place them permanently in parallel is to keep Peukert losses down. This really is not much of an issue below a discharge rate of about C/20 for flooded lead acid batteries. At higher discharge current, say C/10 or above, it begins to be more of a thing. LiFePO4 and some other technologies don't have as much problem with Peukert Effect. If you have for instance three separate banks, 200ah 48v each, and you sometimes crank up the power to 40a, you are pulling C/5 from whichever bank you have online. If the three strings are in parallel, OTOH, you have a total capacity of 600ah and so your 40a draw represents only C/15, and Mr Peukert will be smiling.
With your series strings NOT wired in parallel, you have fewer potential problems and pack balancing is less critical, especially with lead batteries. Most lead users do not have any balancing scheme, they simply manage their bank manually or else they just hook up a 48v smart charger and put it out of their minds. Higher tech batteries should have a proper BMS, Battery Management System, ESPECIALLY with cells in parallel. YMMV, and yeah some will disagree. You will see a lot of vigorous arguments about batteries any time you raise the subject.
Myself, I prefer to not have any batteries in parallel. I don't mind being able to switch them into parallel when desired, though.
So what about your panels? Does each panel feed its own battery through a separate charge controller? If so, yeah you should, IMHO, have some plan for balancing the batteries. You will have masts, antennae, and other things shading the panels so that their output is unequal.
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